Biology is not a difficult portion at all.In fact it is the easiest to understand even for non-science backgrounds.The only tricky thing about Bio is that you have to remember a number of terms and definitions.Once learnt everything else is easy and one only has to understand the process.

I'd suggest that you take a look at the Biology book for class 9 and 10.
Go through it selectively.It has enough material to cover everything related to bio.